The present invention relates to optical pickup devices used in recording/reproducing in an optical recording media, such as a CD (compact disc), a DVD (digital versatile disc), or a Blu-ray disc (registered trademark).
The optical pickup device used in the recording/reproducing in the optical recording media, such as the CD or DVD, or an optical disc drive having the optical pickup device incorporated therein comprises: a first optical system which introduces emitted light from a light emitting element, such as a laser diode, to an objective lens through various kinds of lenses, a prism, a mirror, and the like, and focuses the emitted light on the optical recording medium; and a second optical system which receives returned light from the optical recording medium by means of a photoelectric conversion element for converting an optical output into an electric signal through the objective lens, other various kinds of lenses, the prism, and the mirror. Among them, the optical components, such as various kinds of lenses, need to be fixed to optimum positions with respect to a case of the optical pickup from the optical viewpoint, by using an adhesive.
For an optical disc medium of various standards or an optical disc causing surface blurring due to warping of the disc, the above-described optical pickup device causes an actuator to finely adjust the height of an objective lens and keep a certain distance (a working distance, hereinafter abbreviated as WD) between the objective lens and the optical disc surface, thereby enabling the stable reading or writing of a signal of the optical disc.
Until now, an optical pickup device which is not a thin shape but the so-called “half-height type” among the optical pickup devices does not need a protector member for protecting the disc, being provided so as to be higher than the objective lens in the vicinity of the objective lens of the optical pickup device, because a design to secure a sufficient distance between the optical disc surface and the objective lens surface is possible.
However, the distance between the optical disc surface and the objective lens surface has been decreasing with a reduction in the thickness of a personal computer or the like, and therefore when a focus servo for an actuator deviates or when an external impact force is applied to the optical disc device, the objective lens or the reading surface of the optical disc is damaged and thus a signal cannot be read. Therefore, a low-profile optical pickup device usually employs a structure, in which a protection (protector) member is attached at a position which is protruding toward an optical disc surface side further than the objective lens.
In recent years, an optical pickup device for a Blu-ray disc corresponding to a blue semiconductor laser, or the optical disc drive having the optical pickup device incorporated therein has become conspicuous. In these devices, since the distance between the optical disc and the objective lens decreases further than that in the CD, DVD, or the like, a protector member preventing the objective lens from colliding with the disc and damaging the disc has been required in all of the low-profile, very low-profile, and half-height type optical pickup devices.
As such a protect member, a special POM (polyoxymethylene) or a special fluorine-based molding resin is used which has such an excellent sliding characteristic that will not damage the optical disc surface even if coming into contact with the optical disc surface. These members are characterized in that when coming into contact with the rotating optical disc, the resin thereof itself is easily ground without damaging the optical disc surface, and further that even when an external impact force is applied, these members will not damage the optical disc surface because the contact surface is slippery. Moreover, the objective lens holder is made usually using a liquid crystal polymer or the like from the view point of precision moldability.
Note that, with regard to the optical pickup device, the following patent documents are listed as the prior art documents. JP-A-2006-99814 describes an optical pickup device, wherein a resin capable of serving as a disc protector is fixed around the objective lens and a buffer coating film is applied to the head top of the resin.
JP-A-2008-52812 describes an optical pickup device having a bonded structure in which two types of adhesives are used, one of which is used for the disc protector and the other one is used for preventing the disc protector from peeling off, and further the height of the adhesive for the disc protector is set higher than that of the peeling-off preventive adhesive.
JP-A-2008-269733 describes an optical pickup device, wherein a step is provided at the end of an objective lens, and the objective lens is adhered and fixed to an objective lens holder by applying an adhesive between the objective lens and the objective lens holder.